1. Field of the Invention
This invention relates to semiconductor integrated circuit devices. More particularly, it relates to a technology which is effective when applied to, for example, semiconductor integrated circuit devices employing non-threshold logic circuits.
2. Description of the Related Art
High-speed bipolar type logic LSIs in the prior art are made using ECL (emitter coupling logic) technology. Unlike the ECL circuits which discriminate between high and low logic levels on the basis of a threshold voltage, NTL (non-threshold logic) circuits do not have any specified logic threshold. In NTL circuits, signals are amplified through a plurality of gate circuits. Herein, if the input/output transfer characteristics of the plurality of logical gate circuits intersect substantially at the center voltage, an input level higher than the point of intersection is amplified stepwise, thereby to finally converge to the side of the high level. In each logical gate circuit arrangement, a plurality of logical gates are connected in multistage fashion. Therefore, even when the transfer characteristics of the NTL circuit involve variations, i.e. become altered, the signal has its level corrected by passing through another logical gate circuit having similar variations. Accordingly, any such variations in the transfer characteristics does not develop into a serious problem in practice.
Such an NTL circuit is described in, for example, Genshiki Baba "Saishin Denshi Dabaisu Jiten", Rajio Gijutsu Sha, Mar. 20, 1976, p. 72. In addition, relevant patents are Japanese Patent Publication Nos. 42-21132/1967, 42-2294/1967 and 45-32005/1970.
Although ECL circuits operate at a high speed since the switching of the transistors thereof occurs while they are in an unsaturated state condition and the fact that small amplitudes are involved, they still have the problem of high power-consumption which directly leads to the requirement of high power for the large scale integrated circuits. In contrast, the NTL circuit is of low power-consumption and high operating speed and is accordingly suited to the large scale integration. However, the load driving capacity (capability) thereof is comparatively low.